DESCRIPTION (Taken from application) Hepatitis A virus (HAV) infection is endemic in most of the developing world. With improving conditions, the age of infection shifts from early to later in childhood and adulthood, with increased disease expression an increased morbidity. Regarded as a relatively benign disease in the developed world, there have been reports of HAV being the predominant cause of fulminant hepatic failure (FHF) in childhood in various parts of the developing world, one being Santiago, Chile. HAV's predominant role as the etiology of FHF among children in Santiago is possibly secondary to the endemicity of the infection, with FHF incidence among those with HAV infection, not being significantly different from other parts of the world. True incidence figures for HAV infection and for FHF among those with HAV infection have not been established, making comparison impossible. With entry into a transitional pattern of HAV disease, and an upward shift of the age of HAV infection, an increase in HAV infection morbidity and in FHF secondary to HAV can be expected. The public health implications are great, and substantiation of such a situation would justify concerted intervention, such as universal vaccination. The aims of this project are to determine: 1) the age-specific sero-prevalence and sero-incidence of HA infection in Santiago, Chile, and compare sero-prevalence with previous data; and 2) the age-specific incidence of FHF in Metropolitan Santiago, Chile, in order to estimate the incidence of FHF secondary to and among those with HAV infection, as well as to establish a baseline for future comparison. The study will entail a population-base serosurvey, with repeat serologic testing one year later for those with initial negative HAV serologic tests. Simultaneous active hospital surveillance for FHF is to be performed throughout Metropolitan Santiago. These data should yield estimates of the age-specific sero-prevalence of HAV antibodies, age-specific HAV infection rates, age-specific FHF incidence, and age-specific incidence of FHF among those with HAV infection in Santiago.